A cart moves on an ideal horizontal track

PHYSICS · Multi-part · CBSE · Physics · Laws of Motion · Laws of Motion

Problem

A cart moves on an ideal horizontal track. During a 6 s time interval the net horizontal force

F_x

acting on the cart takes the following constant values: •

0\le t<2\text{ s}:\;F_x=+5\text{ N}

•

2\le t<4\text{ s}:\;F_x=0\text{ N}

•

4\le t\le6\text{ s}:\;F_x=-5\text{ N}

The cart’s initial momentum points in the

+x

–direction. Answer the following questions about the cart’s motion. Assume friction is negligible. (a) Describe how the magnitude and direction of the cart’s momentum change during each of the three time intervals. (b) Compare the total effect of the force acting from

t=0

2\text{ s}

with the total effect of the force acting from

t=4

6\text{ s}

. Explain your reasoning. (c) Based on your answers to parts (a) and (b), state whether the cart’s speed at

t=6\text{ s}

is greater than, less than, or equal to its speed at

t=0

. Justify your conclusion without performing numerical calculations. (d) Sketch a possible graph of momentum versus time for the entire 6 s interval. Label the axes, mark key values of time, and indicate how the slope of your graph relates to the given force values.

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